The present invention is directed to a lamp circuit for an automobile, wherein a transistor provided in a circuit between a power source and the lamp is protected against excessive current when the lamp is short-circuited.
In a lamp circuit of the type having a transistor between the power source and the lamp for intermittently permitting a current to flow through the latter, a short-circuit detector circuit is usually provided to prevent the transistor from being destroyed by a large current when the lamp is short-circuited.
A conventional short-circuit detector detects the short-circuit of the lamp by detecting a variation in the current flowing through a resistor connected in series with the lamp. Due to the voltage drop across the resistor, the voltage applied across the lamp is reduced.
Another conventional short-circuit detector circuit utilizes a resistor connected in parallel with the transistor. However since current flows through the resistor continuously, there is a relatively large current loss.